Aleksey S. Korotkov
Alexander M. Sutin
Inst. of Appl. Phys., Russian Academy of Sciences, 46 Uljanov St., 603600 Nizhny Novgorod, Russia
New methods for the diagnostics of defects in objects made of construction materials, primarily of metals, are proposed. The basic concept of the proposed methods is simple: Materials containing defects have a much larger nonlinear response than materials with no defects. For materials with integrity, the nonlinear responses are up to several orders less as compared with the case of defected materials with defects. It is noteworthy to stress that these nonlinear effects are noticeable even at small strains far from a material damage threshold, thus making it rather attractive for nondestructive testing. The first experiments were performed employing samples shaped as rods made of steel used for fabricating parts of nuclear reactors. The samples were exposed to static stretching in order to introduce defects. Acoustic field modulation was measured by low-frequency vibrations and its increase (more than 30 dB) in stretched samples was observed. The nonlinear interaction of the impact-produced vibrations with the acoustic field in steel samples with a crack was investigated. It was shown that the modulation of sound by such vibration can be used for cracks detection. The method was also used to test a welded joint in a large pipe line for a nuclear power station.